Plasticizers for fibers used to form surgical devices

ABSTRACT

Filaments made from a mixture of absorbable polymers and plasticizers are used to make surgical articles. Preferred plasticizers used in the mixture are stearic acid and its salts.

This application is a continuation-in-part application of U.S. PatentApplication Ser. No. 08/164,510 filed Dec. 9, 1993, now abandoned whichis a continuation-in-part application of U.S. Patent Application Ser.No. 08/095,789 filed Jul. 21, 1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to plasticizers for fibers. Morespecifically, this invention relates to plasticizer/polymer compositionsto be formed into fibers, methods of preparing such fibers, and surgicaldevices made from such fibers.

BACKGROUND OF THE INVENTION

Plasticizers are molecules that when mixed with polar or hydrogen bondedpolymers position themselves between the intermolecular bonds, thusincreasing the spacing between adjacent bonds. In this manner,plasticizers lower the strength of the intermolecular forces, thusincreasing the flexibility of the polymeric structure. For example, PVC,which is polar, is plasticized by substances such as dioctylphthlate. Asanother example, nylon, which is hydrogen bonded, is plasticized bywater. Derivatives of long chain fatty aliphatic acids such as lauric,palmitic, stearic or behenic acid have been identified as spinning aidsfor polyamide fibers. (See, U.S. Pat. No. 3,516,956). Since thesoftening effect of plasticizers is equivalent to increasing extrusiontemperatures, extruding plasticized polymers will require lowertemperatures for comparable melt viscosities. Thus, the danger ofthermal degradation of the polymer is generally decreased by employing aplasticizer. In this respect plasticizers are, indirectly, thermalstabilizes.

Absorbable surgical devices have been made from fibers of syntheticpolymers such as polymer made from glycolide, lactide or p-dioxanone.With respect to polyglycolic acid sutures, U.S. Pat. No. 3,297,033states at column 3, line 45 that: "In general, plasticizers tend tointerfere with crystallinity, orientation, etc., and weaken fibers, butare useful for sponges and films." U.S. Pat. No. 3,792,010 describesplasticized polyester sutures prepared by reacting glycolide and lactidein the presence of a plasticizer such as bis-2-methoxyethyl phthalate oracetoxytriethyl citrate. U.S. Pat. No. 3,636,956 states at column 7,line 9 that any of a variety of plasticizers such as glyceryltriacetate, ethyl benzoate and diethyl phthalate can be used withpolylactide and that preferred plasticizers for glycolide/lactidecopolymers are dibutylphthalate and bis-2-methoxyethyl phthalate. U.S.Pat. No. 4,915,893 describes spinning polyesters such as polylactidewith an additive such as a polyurethane, glycolide, lactide, camphor,benzoic acid-2-hydroxyacetate, hexamethylbenzene, 1,2-cyclohexandioneand other low molecular weight organic compounds which are preferablysoluble in trichlormethane and/or dichlormethane and ethanol and havinga melting temperature in the range of 40° to 180° C.

SUMMARY OF THE INVENTION

It has now been found that fibers useful in making surgical devices canbe prepared by extruding a composition containing an absorbable polymerand a plasticizer selected from the group consisting of stearic acid andits salts. Calcium stearate and stearic acid are particularly preferredplasticizers. In particularly useful embodiments the absorbable polymeris prepared from glycolide, glycolic acid, lactide, lactic acid and/orp-dioxanone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of apparatus which is suitable forcarrying out a preferred fiber manufacturing process in accordance withthe present invention.

FIG. 2A is a schematic illustration of apparatus which is generallysuitable for manufacturing monofilaments of larger size, e.g., size 2 to2/0.

FIG. 2B is a modification of the apparatus of FIG. 2A which is generallypreferred for the manufacture of monofilaments of smaller size, e.g.size 3/0 to 8/0.

FIG. 3 is a perspective view of a suture attached to a needle.

DESCRIPTION OF PREFERRED EMBODIMENTS

Fibers in accordance with the present invention are prepared by spinningor extruding a composition containing a bioabsorbable polymer andplasticizer.

The bioabsorbable polymer can be prepared from any of the monomers knownto form biocompatible, bioabsorbable polymers, such as, for example,glycolide, glycolic acid, lactide, lactic acid, p-dioxanone,epsilon-caprolactone, alkylene carbonates and alkylene oxides. Polymersderived from glycolide, lactide, p-dioxanone or combinations thereof arepreferred.

The plasticizers employed in this invention are selected from the groupconsisting of stearic acid and its salts. In particularly usefulembodiments the plasticizer is stearic acid or calcium stearate.

In preparing filaments in accordance with the present invention, theabsorbable polymer is in a granular, pellet or powder form. The polymercan be prepared in any manner and may, if necessary, be converted to thegranular, pellet or powder form by any conventional means such asgrinding, pulverizing, pelletizing or shredding. Polymerizationtechniques for preparing absorbable polymers are described for examplein U.S. Patent Nos. 3,297,033; 4,052,988; 3,636,956; 4,605,730;4,643,191; 4,653,497; 4,838,267; 5,007,923; 5,019,094; 5,047,048; and5,037,950, the disclosures of which are incorporated herein byreference.

The absorbable polymer may be placed in a hopper and dried. Anappropriate amount of plasticizer is then combined with the polymer andthe polymer and plasticizer are mixed thoroughly to providesubstantially uniform distribution of the plasticizer among the polymerparticles or granules. The amount of plasticizer added may vary fromabout 0.001 to about 5 percent by weight based on the weight of themixture. In particularly useful embodiments the amount of plasticizeremployed is between about 0.01 to 2 percent by weight. Most preferably,the amount of plasticizer is between about 0.02 and 1 percent by weight.

The polymer and plasticizer can be mixed using any conventionaltechnique, with or without heating. For example, a mechanical mixer, astatic mixer or a combination of mixers may be employed to assist inproviding a substantially uniform distribution of plasticizer andpolymer. After mixing, the mixture is extruded or spun to form one ormore filaments.

Known and conventional melt spinning apparatus can be used for theproduction of filaments, in accordance with this invention. FIG. 1schematically illustrates a filament manufacturing operation inaccordance with the invention. Extruder unit 10 is of a known orconventional type and is equipped with controls for regulating thetemperature of barrel 11 in various zones thereof, e.g., progressivelyhigher temperatures in three consecutive zones A, B and C along thelength of the barrel. Pellets or powder of polymeric resin to be spuninto filaments are introduced to the extruder through hopper 12. Priorto being placed in hopper 12, the polymer is combined and mixed with theplasticizer.

Motor-driven metering pump 13 delivers the polymer/plasticizer mixtureat a constant rate through spinneret 15 possessing one or more orificesof desired diameter to provide a plurality of molten filaments 16. Whilespinneret 15 is shown schematically in FIG. 1 as extruding threefilaments, it should be understood that the spinneret may extrudeanywhere from 1 to 200 filaments simultaneously.

The filaments 16 travel downward and are gathered together by guide 19to produce a yarn 17. The distance the filaments 16 travel afteremerging from spinneret 15 to the point where they contact guide 19,i.e., the air gap, can vary and can advantageously be from about 0.5 mto about 10 m and preferably from about 1 m to about 2 m. A chimney 18,or shield, can be provided to isolate filaments 16 from contact by aircurrents which might otherwise affect the cooling or movement of thefilaments in some unpredictable manner. In general, the temperature ofzones A, B and C of the barrel 11 will vary depending on a number offactors such as the chemical nature of the polymer, the size of thepowder or pellets, the nature and amount of plasticizer employed, andthe rate of feed.

Once filaments 16 are gathered together by guide 19 to produce yarn 17,a spin finish may be applied to yarn 17. The spin finish is preferablyapplied to "as spun" filaments (i.e., to filaments which have not beendrawn or otherwise treated, physically or chemically) which have beengathered into a yarn 17. The spin finish can be any desired spin finishcomposition and can be applied using any known technique. As seen inFIG. 1, the yarn 17 may be passed along the edge of applicator 20 towhich the spin finished is supplied at a predetermined rate.

The yarn can be processed in any manner after the application of thespin finish. The spin finish will assist in holding the individualfilaments together, thereby preventing entanglement or separation of thefilaments during subsequent processing. The spin finish also provideslubrication between the yarn and any rollers or godets employed insubsequent processing. In addition, the spin finish will function as aheat transfer medium during subsequent processing, such as drawing, toprovide more uniform heating of the yarn than can be achieved by simplypassing the yarn through heated godets or heated air.

An example of subsequent processing is shown in FIG. 1. Afterapplication of the spin finish, the yarn may be wrapped around a lubegodet 22 and one or more additional godets, for example, godet 23, totake up and adjust the tension on the yarn. The yarn 17 may then bepassed to a heated draw frame 25. Draw frame 25 may be of anyconfiguration. As shown in FIG. 1, draw frame 25 includes three pairs ofgodets which can be used to stretch the yarn or to allow relaxation andperhaps shrinkage of yarn 17. The speed at which the godets rotate andthe temperature at which the draw frame is maintained will determine theamount of stretching and/or relaxation which occurs. Setting the variousspeeds and temperatures to achieve a desired result is within thepurview of those skilled in the art.

Table I provides ranges of values for spinning and stretching parameterssuitable for producing yarns from a composition containing a copolymerof glycolide and lactide and a plasticizer in accordance with thepresent invention.

                  TABLE I                                                         ______________________________________                                        MELT SPINNING APPARATUS                                                       AND OPERATING CONDITIONS                                                                           Copolymer of                                             Apparatus Component, Glycolide and                                            Operating Parameter  Lactide and Plasticizer                                  ______________________________________                                        Extruder barrel temp., zone A, °C.                                                          200-240                                                  Extruder barrel temp., zone B, °C.                                                          210-250                                                  Extruder barrel temp., zone C, °C.                                                          210-250                                                  Extruder barrel pressure, psi                                                                      700-1500                                                 Extruder barrel melt temp., °C.                                                             210-260                                                  Pump size, cc per rev.                                                                              16-.584                                                 Pump rpm              10-40 for size .16 pump                                                       3-11 size .584 pump                                     Pump temp., °C.                                                                             190-250                                                  Pump pressure, psi   500-1500                                                 Pump melt temp., °C.                                                                        190-250                                                  Block temp., °C.                                                                            200-250                                                  Clamp temp., °C.                                                                            200-250                                                  Adapter temp., °C.                                                                          200-250                                                  Candle filter, screen, microns                                                                      10-60                                                   No. of spinneret orifices                                                                           5-200                                                   Diameter of spinneret orifices, .001 in                                                             5-30                                                    Spinneret temp., °C.                                                                        190-250                                                  Spinneret pressure, psi                                                                            500-2500                                                 Spinneret melt temp., °C.                                                                   190-250                                                  cc/hr output, per spinneret orifice                                                                 1-80                                                    First pair of godets, °C.                                                                    50-90                                                   First pair of godets, mpm                                                                           80-200                                                  Second pair of godets, °C.                                                                   60-120                                                  Second pair of godets, mpm                                                                         300-1200                                                 Draw (stretch) ratio  2-8                                                     Third pair of godets, °C.                                                                   ambient                                                  Third pair of godets, mpm                                                                          250-1150                                                 Shrinkage (relaxation), percent                                                                     3-10                                                    ______________________________________                                    

After drawing, the yarn may then be sent to a winder where it can beplaced onto spools for storage while awaiting further treatment or use.

The yarn may be formed into a surgical device using any known techniquesuch as braiding, knitting, weaving, air-entangling, twisting, tying,winding, or forming a composite using the yarn or pieces thereof as areinforcing component.

EXAMPLES

The following Examples 1 and 2 show the preparation of a yarn from 27filaments made from a poly(glycolide-co-lactide) (92.5:7.5 molar ratio;inherent viscosity 1.3-1.45 dl/g) plasticized with calcium stearate(Example 1) and stearic acid (Example 2). For comparison purposes, acontrol yarn of the same absorbable copolymer made by the same processbut containing no plasticizer were also prepared. The spinningconditions for preparing the yarns of the Examples and the control aregiven in Table 2.

                  TABLE 2                                                         ______________________________________                                                            EX-        EX-                                                       CONTROL  AMPLE 1    AMPLE 2                                        ______________________________________                                        Resin Drying 10 hours   10 hours   10 hours                                   Conditions   at 100° C.                                                                        at 100° C.                                                                        at 100° C.                          Additive     None       Calcium    Stearic                                                            stearate   Acid                                       Drying Conditions                                                                          None       12 hours   12 hours                                   for additive            at 120° C.                                                                        at 45° C.                           Percent of   0.000      0.050      0.100                                      Additive                                                                      Spin Finish  20% Lurol in Iso-propanol                                        Die          32 Holes   32 Holes   32 Holes                                   Pump c.c./rev                                                                              0.16       0.16       0.16                                       Filter (micron)                                                                            20         20         20                                         Barrel 1 (°C.)                                                                          218        215      210                                      Barrel 2 (°C.)                                                                          222        218      218                                      Barrel 3 (°C.)                                                                          222        218      218                                      Clamp 1  (°C.)                                                                          214        212      212                                      Mixer    (°C.)                                                                          214        212      212                                      Clamp 2  (°C.)                                                                          214        212      212                                      Adaptor  (°C.)                                                                          210        210      210                                      Block    (°C.)                                                                          210        210      210                                      Pump     (°C.)                                                                          210        210      210                                      Die      (°C.)                                                                          212        210      214                                      Chimney  (°C.)                                                                          100        100      100                                      Chimney Air                                                                            (°C.)                                                                          109        110      110                                      Barrel Melt                                                                            (°C.)                                                                          218        215      215                                      Pump Melt                                                                              (°C.)                                                                          211        205      205                                      Die Melt (°C.)                                                                          219        216      215                                      Screw RPM    1.8        8.5        8.4                                        Pump RPM     19.4       19.4       20.25                                      Lube Pump                                                                              (ml/m)  0.20       0.20     0.20                                     Lube Godet                                                                             (mpm)   133        134      134                                      Godet 1  (mpm)   137        138      136                                      Godet 2  (mpm)   767        769      772                                      Godet 3  (mpm)   750        751      750                                      Barrel   (psi)   970        929      835                                      Pump     (psi)   1000       1000     1000                                     Die      (psi)   577        710      758                                      Average Denier                                                                             43.7       44.2       43.1                                       Average Tenacity                                                                           6.6        7.1        7.2                                        Average Elongation                                                                         21         20         21                                         ______________________________________                                    

The yarn was drawn 5.5 times and then twisted, combined and twistedagain to form a cable-like suture. The cable was then annealed,post-washed and post-treated to remove any residual monomer or othervaporizable impurities. The processing of each of the yarns wasessentially in accordance with the process described in U.S. Pat. No.5,019,093 and U.S. Patent Application Ser. No. 07/855,682, thedisclosures of which are incorporated herein by reference. The physicalproperties of the yarns were tested using the following procedures:

    ______________________________________                                        PROCEDURES FOR                                                                MEASURING PHYSICAL PROPERTIES                                                 Physical Property                                                                         Test Procedure                                                    ______________________________________                                        knot-pull   U.S.P. XXI, <881> tensile strength,                               strength, kg                                                                              surgical suture                                                   straight-pull                                                                             ASTM D2256-88                                                     strength, kg                                                                  elongation at                                                                             ASTM D2256-88                                                     break, %                                                                      tensile strength,                                                                         ASTM D2256-88, Instron Corporation                                kg/mm.sup.2 Model No. 1122                                                    Tenacity    ASTM D2256-88                                                     In Vitro    To simulate in vivo conditons, the suture                         Strength Retention                                                                        samples were stored in a container filled                                     with Sorenson's buffer solution at 37° C.                              After various period of time, the suture                                      samples were then removed from the                                            container to test their knot-pull strength,                                   using an Instron tensile tester. In vitro                                     knot-pull strength retention is indicative of                                 in vivo strength retention.                                       ______________________________________                                    

The physical properties of suture fabricated from the control yarn andsutures made with plasticized filaments in accordance with thisinvention are presented in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                                                          In Vitro                                            Straight-                 Strength                                      Diameter                                                                            Pull  Elongation                                                                           Knot Pull                                                                            Fiber rerention                      Plasticizer                                                                             Denier                                                                             (laser)                                                                             Strength                                                                            at Break                                                                             Strength                                                                             Tenacity                                                                            after 3                 __________________________________________________________________________                                                          weeks                   Example 1                                                                            Calcium Stearate                                                                        950   360 mm                                                                             6.38 kg.                                                                            18.9%  3.54 kg                                                                              7.1 g/d                                                                             55%                     Example 2                                                                            Stearic Acid                                                                            975  .354 mm                                                                             5.97 kg.                                                                            16.7%  3.66 kg                                                                              7.2 g/d                                                                             49%                     Control                                                                              None      963  .347 mm                                                                             6.06 kg.                                                                            18.9%   3.31 kg.                                                                            6.6 g/d                                                                             44%                     __________________________________________________________________________

Monofilaments, rather than multifilament yarn, also can be formed inaccordance with this invention. The monofilament may be used as sutures,or combined with other monofilaments to form a surgical article.

A suitable process for the manufacture of monofilament sutures of thepresent invention comprises the operations of melt extruding a mixtureof resin and plasticizer at an extrusion temperature of from about 170°C. to about 250° C. to provide a monofilament, stretching the solidifiedmonofilament at a temperature of from about 20° C. to about 90° C. inwater (or other suitable liquid medium) or at from about 30° C. to about140° C. in air (or other suitable gaseous medium) at a stretch ratio offrom about 3:1 to about 10:1 to provide a stretched monofilament.Optionally, the stretched monofilament may be stretched again in air orother suitable gaseous medium preferrably at about 130° C. Preferably,the monofilament is then frozen at a temperature of from about -15° C.to about 0° C. The suture may then be annealed at a temperature of fromabout 50° C. to about 130° C. to provide the finished suture.

FIG. 2A schematically illustrates a monofilament suture manufacturingoperation which is especially suitable for producing larger sizesutures, e.g., those of sizes 2/0 and larger. Extruder unit 110 is of aknown or conventional type and is equipped with controls for regulatingthe temperature of barrel 111 in various zones thereof, e.g.,progressively higher temperatures in three consecutive zones A, B and Calong the length of the barrel. Pellets or powder of resins mixed with aplasticizer in accordance with the present invention are introduced tothe extruder through hopper 112.

Motor-driven metering pump 113 delivers melt extruded resin mixture at aconstant rate to spin pack 114 and thereafter through spinneret 115possessing one or more orifices of desired diameter to provide a moltenmonofilament 116 which then enters quench bath 117, e.g., containingwater, where the monofilament solidifies. The distance monofilament 116travels after emerging from spinneret 115 to the point where it entersquench bath 117, i.e., the air gap, can vary and can advantageously befrom about 0.5 to about 100 cm and preferably from about 1 to about 20cm. If desired, a chimney (not shown), or shield, can be provided toisolate monofilament 116 from contact with air currents which mightotherwise affect the cooling of the monofilament in an unpredictablemanner. In general, barrel zone A of the extruder can be maintained at atemperature of from about 100° C. to 220° C., zone B at from about 160°C. to 230° C. and zone C at from about 170° C. to about 240° C.Additional temperature parameters include: metering pump block 113 atfrom about 170° C. to about 230° C., spin pack 114 at from about 170° C.to about 230° C., spinneret 115 at from about 170° C. to about 230° C.and quench bath at from about 10° C. to about 80° C.

Monofilament 116 is passed through quench bath 117 around driven roller118 and over idle roller 119. Optionally, a wiper (not shown) may removeexcess water from the monofilament as it is removed from quench bath117. On exiting the quench bath the monofilament is wrapped around afirst godet 121 provided with nip roll 122 to prevent slippage whichmight otherwise result from the subsequent stretching operation; andsubsequently wrapped around godets 101, 102, 103 and 104 or any othersuitable godet arrangement. Monofilament 116 passing from godet 104 isstretched, e.g., with stretch ratios on the order of from about 3:1 toabout 10:1 and preferably from about 4:1 to about 7:1, to effect itsorientation and thereby increase its tensile strength.

In the stretching operation shown in FIG. 2A, generally suitable forlarger size sutures, e.g., sizes 2 to 2/0, monofilament 116 is drawnthrough hot water (or other suitable liquid medium) draw bath 123 bymeans of godets 124, 105, 106, 107 and 108 or any other suitablearrangement of godets which rotate at a higher speed than godet 104 toprovide the desired stretch ratio. The temperature of hot water drawbath 123 is advantageously from about 30° C. to about 90° C. andpreferably is from about 30° C. to about 50° C.

In the alternative stretching operation shown in FIG. 2B, generallypreferred for smaller sutures sizes, e.g., sizes 3/0 to 8/0,monofilament 116 is drawn by godets 124, 105, 106, 107, and 108 or anyother suitable godet arrangement through hot air convection oven chamber123' at a temperature of from about 30° C. to about 140° C. andpreferably from about 50° C. to about 130° C. to provide the desiredamount of stretch. Following the stretching operation shown in FIG. 2Aor 2B, monofilament 116 optionally may be subjected to an on-lineannealing and/or additional stretching without shrinkage or relaxationwith shrinkage operation as a result of which the monofilament shrinks.In the processes of FIGS. 2A and 2B, on line annealing with or withoutrelaxation when desired is accomplished by driving monofilament 116 bygodets 126, 129, 130, 131, and 132 or any other suitable godetarrangement through second hot air oven chamber 125 at a temperature offrom about 40° C. to about 150° C. and preferably from about 60° C. toabout 130° C. During the relaxation process, at these temperatures,monofilament 116 will generally recover to within about 80 to about 97percent, and preferably to within about 95 percent, of its pre-annealedlength to provide the finished suture. For relaxation, the third godetrotates at a slower speed than the second godet thus relieving tensionon the filament.

Annealing of the suture also may be accomplished without shrinkage ofthe suture. In carrying out the annealing operation, the desired lengthof suture may be wound around a creel and the creel placed in a heatingcabinet maintained at the desired temperature, e.g. about 60° C. toabout 130° C., as described in U.S. Pat. No. 3,630,205. After a suitableperiod of residency in the heating cabinet, e.g., about 18 hours or so,the suture will have undergone essentially no shrinkage. As shown inU.S. Pat. No. 3,630,205, the creel may be rotated within the heatingcabinet in order to insure uniform heating of the monofilament or thecabinet may be of the circulating hot air type in which case uniformheating of the monofilament will be achieved without the need to rotatethe creel. Thereafter, the creel with its annealed suture is removedfrom the heating cabinet and when returned to room temperature, thesuture is removed from the creel, conveniently by cutting the woundmonofilament at opposite ends of the creel. The annealed sutures,optionally attached to surgical needles, are then ready to be packagedand sterilized.

The suture of the present invention, suture 201, may be attached to asurgical needle 200 as shown in FIG. 3 by methods well known in the art.Wounds may be sutured by passing the needled suture through tissue tocreate wound closure. The needle preferably is then removed from thesuture and the suture tied.

EXAMPLE 3

A monofilament is made from a copolymer of glycolide and lactidecontaining about 18 weight percent glycolide and about 82 weight percentlactide. The production of the copolymer is described in U.S. Patent No,the disclosure of which is incorporated herein by reference. The resinis mixed with 3% by weight of calcium stearate and extruded intomonofilaments of size using the following conditions:

    ______________________________________                                        CONDITIONS OF                                                                 MANUFACTURING PLASTICIZED MONOFILAMENT                                        Process Conditions                                                            ______________________________________                                                             Extrusion Operation                                      extruder screw, rpm  2.2                                                      pump rpm             12.7                                                     driven roller, mpm   2.7                                                      barrel temp., °C., zone A                                                                   115                                                      barrel temp., °C., zone B                                                                   180                                                      barrel temp., °C., zone C                                                                   183                                                      clamp temp., °C.                                                                            182                                                      adapter temp., °C.                                                                          183                                                      pump temp., °C.                                                                             183                                                      barrel melt temp., °C.                                                                      177                                                      pump melt temp., °C.                                                                        179                                                      Spinneret melt temp., °C.                                                                   180                                                      barrel pressure, psi 1040                                                     pump pressure, psi   500                                                      pump size, cc per revolution                                                                       0.16                                                     diameter of spinneret orifices, mm                                                                 1.25                                                     no. of spinneret orifices                                                                          1                                                        quench bath temp., °C.                                                                      18                                                       depth of driven roller, cm                                                                         19                                                                            Stretching                                                                    Orienting Operation                                      first draw oven temp, °C.                                                                   126                                                      first godet station, mpm                                                                           4.0                                                      second godet station, mpm                                                                          22.4                                                     second oven temp., ¤C.                                                                    130                                                      third godet station, mpm                                                                           29.5                                                     draw ratio           7.4:1                                                    ______________________________________                                    

For comparison purposes, a control monofilament was prepared using thesame copolymer and the same extrusion and stretching conditions,however, the control monofilament was made without plasticizer. Bothmonofilaments were annealed at 90° C. for 18 hours in a nitrogen oven.

The physical properties of the monofilament of Example 3 prepared inaccordance with the present invention and the control monofilament arepresented in Table 4.

                  TABLE 4                                                         ______________________________________                                                    Knot-Pull                                                                             Straight Pull                                                         (kpsi)  (kpsi)                                                    ______________________________________                                        Example 3     40        62                                                    Control       34        60                                                    ______________________________________                                    

As the data presented in Table 4 shows, the monofilament of Example 3exhibited both higher knot-pull and straight-pull tensile strengthcompared to the control monofilament.

Obviously, other modifications and variations of the present inventionare possible in light of the above teachings. For example, multifilamentyarns may be formed rather than monofilaments. The monofilaments may beused as sutures, or combined with other monofilaments to form a surgicalarticle. It is therefore to be understood that changes may be made inparticular embodiments of the invention described which changes arewithin the full intended scope of the invention as defined by theclaims.

What is claimed is:
 1. A method of making a surgical articlecomprising:a. providing a mixture comprising an absorbable polymer and aplasticizer selected from the group consisting of stearic acid and itssalts; b. forming at least one filament from said mixture; and c.forming a surgical article from said at least one filament.
 2. A methodof making a surgical article comprising:a. providing a mixturecomprising an absorbable polymer and a plasticizer selected from thegroup consisting of stearic acid and calcium stearate; b. forming atleast one filament from said mixture; and c. forming a surgical articlefrom said at least one filament.
 3. A method as in claim 1 wherein saidabsorbable polymer is selected from the group consisting of polymersmade from one or more of glycolide, glycolic acid, lactide, lactic acid,epsilon-caprolactone and p-dioxanone.
 4. A method as in claim 1 whereinsaid absorbable polymer is a copolymer of glycolide and lactide.
 5. Amethod as in claim 1 wherein said absorbable polymer comprises repeatingunits of p-dioxanone.
 6. A method as in claim 5 wherein said absorbablepolymer is a homopolymer of p-dioxanone.
 7. A method as in claim 5wherein said absorbable polymer is a copolymer containing repeatingunits of p-dioxanone.
 8. A method as in claim 7 wherein said copolymeris a block copolymer.
 9. A method as in claim 1 wherein said plasticizeris calcium stearate.
 10. A method as in claim 1 wherein said step ofproviding a mixture comprises:a. providing particles of absorbablepolymer; b. combining said plasticizer with said particles; and c.mixing the particles and plasticizer together to provide a substantiallyuniform distribution of plasticizer among the particles.
 11. A method asin claim 1, wherein the step of forming at least one filament comprisesmelt spinning the mixture.
 12. A method as in claim 1, wherein the stepof forming a surgical article comprises attaching a surgical needle to asingle filament.
 13. A method as in claim 1, wherein a plurality offilaments are formed in the step of forming at least one filament fromthe mixture.
 14. A method as in claim 13, wherein the step of forming asurgical article comprises gathering the plurality of filaments to forma yarn.
 15. A method as in claim 13, wherein the step of forming asurgical article comprises attaching a needle to the plurality offilaments.
 16. A method as in claim 1, wherein the mixture contains fromabout 0.001 to about 5 percent of the plasticizer based on the weight ofthe mixture.
 17. A method as in claim 1, wherein the mixture containsfrom about 0.02 to about 1 percent of the plasticizer based on theweight of the mixture.
 18. A method making a surgical articlecomprising:a. providing a mixture containing an absorbable polymer and aplasticizer selected from the group consisting of stearic acid andcalcium stearate; b. extruding the mixture to form a filament; and c.forming a surgical article from the filament.
 19. A method as in claim18 wherein the step of extruding the mixture comprises melt spinning themixture to form a filament.
 20. A method as in claim 18 wherein aplurality of filaments are formed from the mixture in the extrudingstep.